— A pure substance has no other substance mixed with it
— Purity is important for stuff like food, drugs, vaccines
— An unwanted substance mixed with the substance you want is called an impurity
— Impure substances have a range of melting and boiling points
— The wider the range of melting and boiling points, the more impure the substance is
— Impure substances = melting point lower, boiling point higher
Why? To obtain the specific substance we need, to retain the pure substance!